1. Field of the Invention
The present invention relates to a recording apparatus, and relates in particular to a recording apparatus that cleans a recording drum or an image receiving sheet by removing foreign substances therefrom.
2. Description of the Related Arts
A recording apparatus according to the present invention fixes to a recording rotary drum (hereinafter referred to as a recording drum), or to a recording plane, a recording medium (a general term used for an image receiving sheet that is fixed to a recording drum, and a toner sheet that is fixed to and covers the image receiving sheet), and records an image on the recording medium by irradiating it with a laser beam emitted by an optical head.
FIG. 13 is a schematic diagram illustrating the overall recording apparatus according to the present invention.
In FIG. 13, in order to produce a full-color image, a recording apparatus 30 comprises: a recording medium supply unit 32; a recording drum 34; a recording medium holding/releasing mechanism 36, which is provided on the recording drum 34; a laminating mechanism 38, arranged externally around the recording drum 34; an exposure head 40; a peeling mechanism 42; a paper supply unit 44; a laminating unit 46; a fixing unit 48; a separation unit 50; a tray unit 52; and a controller 54.
The recording apparatus 30 feeds an image receiving sheet R and a toner sheet T from the recording medium supply unit 32 to the recording drum 34. The recording medium holding/releasing mechanism 36 then fixes the image receiving sheet R to the recording drum 34, following which the laminating mechanism 38 applies thermal pressure to laminate the toner sheet T and the image receiving sheet R. Depending on the type of recording medium used, this heat lamination process may not be required.
Then, a latent image is formed on the toner sheet T by irradiating the recording medium with a heat mode laser beam emitted by the exposure head 40, which is operated, in consonance with an image signals, by the controller 54. Following this, the peeling mechanism 42 separates the toner sheet T from the image receiving sheet R on the recording drum 34 and the latent image on the toner sheet T is transferred to and developed on the image receiving sheet R.
This process is repeated several times to transfer three or four colors, and after a color image has finally been formed on the image receiving sheet R, the laminating unit 46 presses a paper sheet H, which is supplied from the paper supply unit 44, and the image receiving sheet R together so that they adhere to each other. Following this, the fixing unit 48 optically cures an image receiving layer 66 on the image receiving sheet R and the separation unit 50 removes the image receiving sheet R from the paper sheet H. Then, the paper sheet H, to which the full-color image is fixed, is output to a proof tray 52a, while the used image receiving sheet R is discharged to a waste stacker 52b.
In this manner, a full-color, hard copy of the image can be obtained.
The recording medium supply unit 32 comprises: a recording medium station 53, for holding recording medium stock (i.e., a roll of image receiving sheet R stock, and a plurality of rolls of photosensitive toner sheet T stock in such standard colors as black (K), cyan (C), magenta (M) and yellow (Y), or in special colors such as the gold and silver that are used in the printing industry); a pair of feed rollers 54, for feeding one type of recording medium stock; a cutter 55, for cutting the recording medium stock to form a sheet after the feed rollers 54 have extracted a specified length of stock from the recording medium station 53; a pair of rollers 56, for holding and transporting the thus formed recording sheet; and a guide 57, along which the recording sheet is conveyed, toward the recording drum 34, until the leading end of the recording medium reaches a fixed position at the recording medium holding/releasing mechanism 36, which is attached to the recording drum 34.
An image receiving sheet R is supplied first to the recording drum 34, and its leading edge is secured by clamps that constitute part of the recording medium holding/releasing mechanism 36. Then, an image receiving sheet R is fitted around the recording drum 34, as it rotates in the direction indicated by an arrow, so that the trailing edge can also be secured by the mechanism 36. At this time, it is preferable that at the least either the leading end fixing portion or the trailing edge fixing portion of the recording medium holding/releasing means 36 be permitted to slide along the outer surface of the recording drum 34, so that recording sheets of various lengths can be accommodated by the recording drum 34.
Following this, in the same manner as is described above, a toner sheet T, which is obtained from the recording medium supply unit 32, is fitted around the recording drum 34 and is laminated with the image receiving sheet R that was previously positioned around the outer surface of the recording drum 34. The lamination of the toner sheet T and the image receiving sheet R is performed by a laminating roller 58, which incorporates a heater (not shown); an arm 59, which pivots at a fulcrum 59aand which moves and positions the laminating roller 58 so that it contacts the outer surface of the recording drum 34 or is moved away from the surface of the recording drum 34; and pressing means 60, which applies a predetermined pressure to force the laminating roller 58 against the outer surface of the recording drum 34. The pressing means 60 is urging means, such as a spring, and may be an operator for an air cylinder.
Since an adhesive coating is applied to the outermost image receiving layer 66 of the image receiving sheet R, the toner sheet T can be applied to and laminated with the sheet R by employing the predetermined pressing force to hold the laminate roller 58 against the sheets. As a result, no creases are formed in the toner sheet T, and the image receiving layer on the image receiving sheet R closely and uniformly adheres to a toner layer on the toner sheet T.
In this case, the laminating roller 58 is used to laminate the toner sheet T and the image receiving sheet R because the sheets must uniformly adhere to each other. However, in order to increase the strength of the adhesion established between the sheets, it is preferable that, in addition to the pressure applied by the laminating roller 58, a thermal lamination process be performed. The temperature used should be equal to or lower than 130.degree. C., and preferably should be equal to or lower than 100.degree. C.
In addition, when the image receiving sheet R is to be positioned around the recording drum 34, it is preferable that the leading edge of the image receiving sheet R be secured by the recording medium holding/releasing mechanism 36, and that the other portion of the sheet R be held by the feed roller pair 56, the laminating roller 58 or another means, so that a predetermined tension is applied to the image receiving sheet R. In this case, as will be described later, suction holes may be formed around the outer surface of the recording medium 34, and suction applying means may be used to produce a suction effect that holds the image receiving sheet R against the surface of the recording drum 34 (see FIG. 14). While it is preferable that the suction means and the recording medium holding/releasing mechanism 36 be employed together, each of them can be employed individually. As a result, the image receiving sheet R can be secured to the outer surface of the recording drum 34 without any creases being formed in it and without its position being shifted during the process. It is also preferable that tension be applied to the toner sheet T when it and the image receiving sheet R are laminated. In the same manner as when the image receiving sheet R is positioned, the recording medium holding/releasing mechanism 36 may be employed to secure the leading edge and/or the trailing edge of the toner sheet T, or it and the above described suction means may be employed together. It should be noted that, preferably, less tension is applied to a toner sheet T during the lamination process than is applied to an image receiving sheet R when it is positioned around the recording drum 34.
The exposure head 40 comprises modulation means; a laser head 24, which includes a laser beam source that emits a high-density energy beam (a laser beam), and an image focusing lens, for adjusting the diameter of the spot produced by a laser beam; and secondary scanning means 61, for moving the laser head 24 in the axial direction of the recording drum 34 (direction vertical to the paper surface in FIG. 1) to perform secondary scanning.
The primary scanning of the toner sheet T, for which a laser beam is used, is performed by the rotation of the recording drum 34. And instead of the secondary scanning means 61 being provided for the exposure head 40, moving means for displacement in the axial direction may be provided for the recording drum 34, and the secondary scanning may be performed and move the recording drum 4 at the same time it is being rotated for the primary scanning.
The laser beam source need only emit a high-density energy beam that enables heat mode exposure, and can be, for example, a gas laser, such as an argon ion laser, a helium neon or a helium cadmium laser, a solid-state laser such as a YAG laser, a semiconductor laser, a color laser, or an excimer laser. Modulation of a laser beam in accordance with an image signal is performed by a well known method, such as a method for transmitting a laser beam to an external modulator when an argon laser is employed as a laser beam source, or a method for using a signal to control (directly modulate) a current that flows to a laser when a semiconductor laser is employed as the laser beam source. The size of a laser spot focused on a photo-thermal conversion layer, and the scanning speed are determined in accordance with the resolution required for an image and the recording sensitivity of the scanned material. For printing, generally a high resolution is required, and for image quality a small beam spot is preferable. However, the focusing depth is short and providing efficient mechanical control is difficult. In addition, when the scanning speed is reduced to a point at which it is too low, heat loss due to the conduction of heat to the toner support member is increased, the energy efficiency is deteriorated, and the recording time is extended. From this it has been concluded that for this invention the recording conditions should be: a beam spot on the photothermal conversion layer of 5 to 50 .mu.m, preferably 6 to 30 .mu.m, and a scanning speed of 1 m per second or higher, preferably 3 m per each second or higher.
An image signal from an external image reader for the recording apparatus 30, from an image processor, from a workstation (W/S) having a DTP function, from an electronic publishing system, or from various storage media (a magnetic tape, a floppy disk, a hard disk, a RAM card, etc.) is transmitted to the controller 54, via an interface, as a digital signal. Necessary processing is performed for the image signal, and the resultant image signal is transmitted to the exposure head 40 to provide control for the head mode exposure process performed by the laser head 24.
The controller 54 controls the secondary scanning performed by the secondary scanning means 61 of the exposure head 40 and the rotation of the recording drum 34 for primary scanning, and also controls the operation of the individual sections of the recording apparatus of this invention as well as all functions performed during the processing sequence.
The peeling mechanism 42 separates, from the image receiving sheet R, the toner sheet T on which a latent image has been formed by the heat mode exposure process performed by the exposure head 40, and at the same time transfers the latent image from the toner sheet T to the image receiving sheet R for development. The peeling mechanism 42 includes: a separation roller 62; two division rollers 63 and 64, which abut upon the separation roller 62; a comb-toothed guide plate 65, which is located along the separation roller 62 and between the division rollers 63 and 64; and a bracket (not shown) on which these integrally provided components are mounted. The separation roller 62 is supported by an arm 67, and pivots at a fulcrum 67a so that it can brought into contact with or separated from the recording drum 36. In addition, pressing means 68 is provided that employs the arm 67 to press the separation roller 62 against the laminated image sheet R and toner sheet T on the recording drum 34.
After thermal energy has been applied during the heat mode exposure process, and a latent image has been formed on the toner sheet T by reducing the adhesive strength of the toner layer 22, the arm 67 is rotated at the fulcrum 67a and the bracket is brought in contact with the lamination of the toner sheet T and the image receiving sheet R on which is deposited the image receiving layer 66. Then the comb-toothed guide plate 65 is inserted between the image receiving layer 66 on the image receiving sheet T and the toner layer 22 on the toner sheet T, and from the tone sheet T side, pressure is applied to the laminate by the separation roller 62. If the length of either the toner sheet T or the image sheet R has changed, the comb-toothed guide plate 65 can be easily inserted between the two. Following this, as the recording drum 34, as well as the separation roller 62 and the division rollers 63 and 64, is rotated the leading edge of the toner sheet T is moved along the comb-toothed guide 65 until it is held between the separation roller 62 and the division roller 63. The toner sheet T, to which pressure is applied by the separation roller 62, is transported while sandwitched between the separation roller 62 and the division rollers 63 and 64 until it is finally separated from the image sheet R. Since the toner sheet T can be separated at a constant speed at the portion to which pressure is applied by the separation roller 62, a constant force can also be-applied for peeling, so that a phenomenon such as stick slipping does not occur and uniform peeling can be performed. Furthermore, since the separation force applied to the image receiving sheet R does not vary, the image receiving sheet R held in a fixed position on the recording drum 34 and is not shifted. Accordingly, deterioration of the alignment accuracy does not occur. As a result, a single-color, gray scale dotted image, having a high image quality and a high resolution, can be obtained for which peeling is performed uniformly and for which no alignment shifting occurs.
The image receiving sheet R, on which images of C, M, Y and K colors are precisely aligned and for which separation, transferring and developing have been performed, is fed by a transfer roller pair 71 along guide members 70 to the laminating unit 46.
At the laminating unit 46, as the image receiving sheet R is fed in, a main sheet H from a paper cassette 73 is supplied by a paper supply roller 72 and is fed along the guide member 70 on the left in FIG. 13. The main sheet H may also be fed to the paper supply roller 72 through a manual supply port 44a. Then, the image receiving sheet R and the main sheet H are positioned and laminated by a resist roller pair 75, and the laminate is transferred to the fixing unit 48.
The laminating unit 46 may be provided separately from the recording apparatus 30.
In the fixing unit 48, the image receiving sheet R and the main sheet H, which have been laminated by the laminating unit 46, are thermally secured to each other by a thermal fixing roller pair 76 consisting of a pressing roller 76a and a heating roller 76b. The sheet laminate is fed between the rollers 76, and is cured by a post-exposure lamp 77, such as an ultraviolet lamp, so that the image receiving layer 66 on the image receiving sheet R can be easily separated from the sheet H.
Depending on the recording medium type, the fixing process may not be required.
Next, at the separation unit 50, the image receiving layer which has been cured and is ready to be separated, is peeled off the image sheet R by a separation roller pair 78 and a separation guide 79, and by adhering to the main sheet H transfers the image to it. Subsequently, the image bearing sheet H is output as hard copy to the proof tray 52a of the tray unit 52, while the image receiving sheet R, from which the image receiving layer 66 has been separated, is discharged to the waste tray 52b.
As is described above, the recording apparatus 30 in FIG. 13 fixes a recording medium to the recording drum 34 for printing. However, since the recording drum 34 rotates at a comparatively high speed during the recording process, sometimes the recording medium may be lifted away from the recording drum 34, and shifted or curled.
In order to prevent this, a suction device shown in FIG. 14 is used to hold the recording medium. FIG. 14A is a conceptual cross-sectional view of this suction device, and FIG. 14B is a perspective view of the surface of a recording drum in which multiple suction holes have been formed.
In FIGS. 14A and 14B, the suction device comprises: a recording drum 11, suction holes 142, rotary shaft holes 143, a suction pipe 144 and an air blower 145. The multiple suction holes 142 are radially formed in the recording drum 34 within an area to which a recording medium 10 is fixed. The recording drum 11 is hollow, and the multiple rotary shaft holes 143 are formed in the rotary shaft. The recording drum 11 is connected via the suction pipe 144 to the air blower (or a vacuum pump) 145, which is an external suction source. While the size of suction holes 142 is exaggerated in the drawings so that they can more easily be seen, in actuality, more and smaller holes are formed.
When the air blower 145 begins to produce suction, air from the recording drum 11 is drawn into the suction pipe 144, and the internal pressure of the recording drum 11 is thereby reduced. Thus, the recording medium 10 is drawn to and securely held on the surface of the recording drum 11 by the vacuum effect established by the suction of air through the multiple suction holes 142.
More specifically, as previously described, the recording medium 10 consists of the image receiving sheet R and the toner sheet T. And first, when the image receiving sheet R is positioned on the recording drum 11, it is held there by the vacuum effect produced by the suction of air through the arrangement of multiple suction holes 142 under it. Then, when the toner sheet T is placed over the image receiving sheet R, since the toner sheet T is cut so that it is larger than the image receiving sheet R, portions of it extend outward, on all four sides, beyond the edges of the image receiving sheet R, and are attracted by the vacuum at the multiple suction holes 142 that lie under them. As a result, the toner sheet T is also fixed to the recording drum 11.
In this case, when the toner sheet T covers the image receiving sheet R, creases may be formed at the ends of the toner sheet T due to the thickness of the image sheet R. Since such creases adversely affect the recording process, the formation of creases must be prevented.
Therefore, as will be described later, a step portion is provided for the recording drum 11 by (1) attaching step tape to the surface of the recording drum 11, or (2) by forming a groove in the surface of the recording drum 11, and the height of the step portion is set so that it is substantially equal to the thickness of the image receiving sheet R. Then, when the toner sheet covers the image receiving sheet, no creases are formed at the ends of the toner sheet. In this case a recording drum 11 is employed on which, to prevent the formation of creases, a step portion can be formed by attaching step tape to or by forming a groove in the surface.
The attachment of dust, which can result in a recording failure, still constitutes a problem for such a recording apparatus. There are two types of recording failures that occur due to the attachment of dust:
(1) a recording failure that occurs when dust is attached to the image receiving sheet (occurrence of a so-called blank area); and PA1 (2) a recording failure that occurs when dust is attached to the recording drum (occurrence of a so-called blank ring).
FIG. 15 is a diagram for explaining the reason for the occurrence of a blank area recording failure (1).
In FIG. 15, an image receiving sheet R is fixed to the surface of the recording drum (hatched portion), the toner sheet T is fixed thereto, and dust X is trapped between the sheets R and T.
When dust X is present on the image receiving sheet R, an adhesion failure due to the dust X occurs between the toner sheet T and the image receiving sheet R, and an image nonexistent area (a so-called blank area) occurs spanning a range A described by an arrow A.
FIG. 16 is a diagram for explaining the reason that a recording failure (2), a blank ring, occurs. In this case, when an image receiving sheet R and a covering toner sheet are fixed to the surface of the recording drum (hatched portion), dust X is trapped between the recording drum and the image receiving sheet R.
When dust X is present on the recording drum, the image receiving sheet R, which is strongly attracted by the vacuum produced at multiple suction holes, assumes a shape resembling that of the dust X. However, the vacuum produced attraction affecting the toner sheet T is strong only at the portions that overlap the image receiving sheet R, and is weak and has little effect on the toner sheet T at the location of the dust X. In this case, since the toner sheet T is rigid to a degree, a ring-shaped gap C is formed between the toner sheet T and the image receiving sheet R in the area surrounding the dust X, even though at the center of the area in which the dust X is located the toner sheet T and the image receiving sheet R closely adhere to each other. Therefore, because of this gap C the image can not be transferred, and a blank, ring-shaped band (a so-called blank ring) is produced within the range described by an arrow B.
Further, because of the misalignment of the image receiving sheet R and the toner sheet T that is caused by the dust X, the point of focus of a recording laser beam L is shifted, a satisfactory energy intensity can not be obtained, an image is tapered off across the range described by the arrow B, and the image density image is reduced, resulting in the production of a coarse image.
To resolve this problem, a roller having a more adhesive surface (hereinafter referred to as an adhesive roller) is employed as the laminating roller 58 in FIG. 13. As the adhesive roller is rotated, the portion in contact with the image receiving sheet R removes dust therefrom.
But when such a adhesive roller was employed to remove dust from an image receiving sheet R positioned on a conventional recording drum to which step tape was attached, the following problem was encountered.
FIG. 11A or 11B is a front cross-sectional view and a side sectional-view of provided for a recording drum 1 on which is mounted step tape 3. In FIG. 11A, an image receiving sheet 4 is fed to and fixed on the recording drum 1. In FIG. 11B, a toner sheet 5 is fed the recording drum 1 and secured to the image receiving sheet 4 in FIG. 11a.
Generally, the external width of the image receiving sheet 4 is smaller than the internal width of the step tape 3, and the external width of the toner sheet 5 is greater than that of the image receiving sheet 4, in order to increase the adhesive strength between it and the image receiving sheet 4.
In FIG. 11, a adhesive roller 2 is located near, and step tape 3 is attached to the recording drum 1, which is rotated so that the recording medium (i.e., the image receiving sheet and the toner sheet) can be fitted around it. The adhesive roller 2 is located near the recording drum 1, so that it can contact the image receiving sheet 4, and two lengths of the step tape 3, are attached, in the rotational direction, around the left and right portions of the outer surface of the recording drum 1, and two more lengths are extended, in the axial direction, near the ends of the first two lengths. During the image recording process, the image receiving sheet 4 is fed to the recording drum 1 and is secured to the area defined by the inner side of the step tape 3 (the inner side of the step tape 3 delineates an area between steps, i.e., an area enclosed by lengths of the step tape 3 that are attached in parallel, in the rotational direction, to the right and left portions of the outer surface of the recording drum 1 and are attached in parallel, in the axial direction, near both ends of the first lengths). The toner sheet 5, the size of which does not exceed the outer limits of the step tape 3, is fed to the recording drum 1 and adheres to the image receiving sheet 4 and the step tape 3.
As the adhesive roller is rotated in contact with the image receiving sheet 4, dust is removed from the image receiving sheet 4.
As is shown in FIG. 11A, the image receiving sheet 4 is fed to the rotating recording drum 1, and is positioned around and secured to the recording drum 1 while the adhesive roller 2 above the recording drum 1 follows the contours of the image receiving sheet 4.
Then, as is shown in FIG. 11B, the toner sheet 5 is fed to the recording drum 1, on which the image receiving sheet 4 is positioned, and is attached to the image receiving sheet 4 by a suction produced vacuum. At this time, if step tape 3 is not attached to the recording drum 1 or if the toner sheet 5 is longer than the outer size of the step tape 3, the height difference produced by the image receiving sheet 4 or the step tape 3 causes the end of the toner sheet 5 to be folded over so that a crease is formed in it and a uniform image can not be obtained. Therefore, the width and length of the toner sheet are larger than those of the image receiving sheet, but are smaller than those delineated the by outer size of the step tape.
A recording drum in which a groove is formed will now be described while referring to FIGS. 12A and 12B.
FIGS. 12A and 12B are a front sectional-view and a side sectional-view of a adhesive roller provided for a conventional recording drum 1 in which a groove is formed. In FIG. 12A, an image receiving sheet 4 is fed to and held on the recording drum 1, and in FIG. 12b, a toner sheet 5 is fed to and held on the image receiving sheet 4 in FIG. 12A.
In FIGS. 12A and 12B, a adhesive roller 2 is located near the recording drum 1, which is the same as the one shown in FIGS. 11A and 11B, with the exception that instead of step tape being attached to its surface, a groove is formed in it. An image receiving sheet 4 is fed to the groove and is secured therein, and a toner sheet 5 is fed to the recording drum 1 and adheres to the image receiving sheet 4. Using the groove, a step portion is formed on the recording drum 1.
Generally, the width of the image receiving sheet is smaller than the internal size of the groove, and the toner width is greater than the widths of the image receiving sheet and of the groove in the recording drum.
However, for a recording drum 1 to which step tape 3 is attached or in which a groove is formed, if the step tape is thicker than the image receiving sheet 4, or if the depth of the groove in the recording drum 1 is greater than the thickness of the image receiving sheet 4, i.e., if the image receiving sheet 4 is thinner than a predetermined thickness when the sheet is changed, dust can not efficiently be removed from the image receiving sheet 4 since the adhesive roller 2, which at both ends contacts the step tape 3 or the recording drum 1, does not uniformly contact the image receiving sheet 4. If the adhesive roller 2 and the recording drum 1 contact each other, even though the thickness of the step tape 3 (or the depth of the groove) is the same as that of the image receiving sheet, the force applied at the center portion is stronger than the force applied at the ends, so that the adhesive roller does not contact the image receiving sheet 4 evenly, and dust on the image receiving sheet 4 can not be uniformly removed.
Further, as is described above, while dust on an image receiving sheet can be removed by using the adhesive roller 2, dust on a recording drum 1 in which a step is formed can not removed by using the adhesive roller.